Study On Pickering Emulsions Stabilized By Enzyme-Immobilized Alginate Microparticles For Interfacial Catalysis In Biphasic System

Pickering emulsions are a type of emulsion which stabilized by solid particles.Compared with emulsions stabilized by surfactant,Pickering emulsion has the advantages of high stability,low toxicity,green and environmental friendliness,thus it is widely used in the field of biocatalysis between two phases.The silanized TiO₂ nanoparticles?s-TiO₂?are coated on the surface of alginate microspheres by emulsion polymerization to prepare an alginate microsphere?Alg@s-TiO₂?with tailored wettability,The microspheres can stabilize Pickering emulsion and act as a carrier for the enzymatic catalysis at the oil-water interface.In this thesis,the mechanism of Pickering emulsions stabilized by alginate microspheres and the application of the biphasic interfacial catalysis are studied.In the part of preparation of Alg@s-TiO₂ microspheres and used to stabilized Pickering emulsion,we study the hydrophobically modification of alginate microspheres and the mechanism of stabilized Pickering emulsion.The s-TiO₂ nanoparticles are prepared by hydrophobic modification of TiO₂ nanoparticles by alkylsilane,then,s-TiO₂ nanoparticles are coated on the surface of alginate microspheres by electrostatic adsorption during the emulsion polymerization process,thus the alginate microspheres obtain suitable oil-water amphiphilicity?three-phase contact angle?is closed to 90^o?.The whole process is green and mild.The results show that the modified TiO₂ nanoparticles are aggregated into agglomerates with 150 nm and coating on the surface of the alginate microspheres.The different wettability of s-TiO₂ nanoparticles can be changed with the carbon number of the modified reagent.The wettability of Alg@s-TiO₂ microspheres has the same tendency as that of s-TiO₂ nanoparticles,when the?increases,the effect of both stable emulsions decreases.This research can be applied in the fields of biomedicine,cosmetics,food industry and enzyme engineering.In the part of water-in-oil Pickering emulsion-enhanced interface catalytic reaction,based on the preparation of Alg@s-TiO₂ microspheres,Lipase from Candida sp.recombinant,expressed in Aspergillus Niger?CALB?is encapsulated in the interior of Alg@s-TiO₂microspheres to obtain E@Alg@s-TiO₂ microspheres.The microspheres are used to stabilize Pickering emulsion for the enzymatic reaction in water/hexane system.The results show that the lipase immobilization efficiency of 17%and loading amounts of 16 mg/g?lipase/Alg@C6-TiO₂?through a mild and green gelation process.The Pickering emulsion stabilized E@Alg@s-TiO₂ microsphere are proved to be water-in-oil type.The effect of E@Alg@s-TiO₂ microsphere concentration on emulsion stability was studied,with the increase of microsphere concentration from 0.5² wt%,the emulsion droplet diameter decreases and stability increases.The stable Pickering emulsion can be stored for more than one year.By comparing the esterification reaction of the lipase in the inner aqueous phase of Pickering emulsion and the conventional biphasic system,the conversion and specific activity of E@Alg@s-TiO₂ has an obvious improved effect,because of a reduced diffusion distance of these molecules and the protection of the alginate microspheres and the surface TiO₂nanoparticles.The Pickering emulsion can be repeat 10 cycles for a total of 240 h and keep the above 90%of initial enzyme activity.The research results provide a new method for the application of biphasic catalysis of water-in-oil Pickering emulsion.In the part of oil-in-water Pickering emulsion-enhanced interface enzyme-catalyzed reaction,the authors tried to use E@Alg@s-TiO₂ microspheres to stabilize paraffin oil/water Pickering emulsion for the hydrolysis of tributyrin.We find that the?of E@Alg@C6-TiO₂microspheres is 100^o,and stabilize O/W Pickering emulsion when the oil-water ratio is 1:1.2.The effect of E@Alg@s-TiO₂ microsphere concentration on emulsion stability is studied.The emulsion droplet diameter is reduced and the stability is improved by the concentration of microsphere is increased from 1³ wt%.By comparing the hydrolysis reaction of the enzyme in the aqueous phase of the Pickering emulsion and the biphasic system,it can be found that the Pickering emulsion system stabilized by E@Alg@s-TiO₂ microspheres has excellent strengthening effect.The immobilized enzyme activity of the emulsion system is 1.2 and 7.8times higher than that of free enzyme in emulsion system and biphasic system,the stable Pickering emulsion can maintain 80%of the initial enzyme activity during repeated use of 5cycles?10 h per cycle?.The research can be applied in the variety of the biocatalysis of oil-water Pickering emulsion.